Free or Total Chlorine, which to test?

[reefiniteasy]

Should I be testing free or total chlorine so I know if my carbon block is exhausted on my RODI?

I bought total chlorine test strips and tested my tap and RODI and both came up 0. I’m not sure the test strips were accurate, there has to be chlorine in the school’s tap water, right?

Just need some advice.

 

[DSEKULA]

Should I be testing free or total chlorine so I know if my carbon block is exhausted on my RODI?

I bought total chlorine test strips and tested my tap and RODI and both came up 0. I’m not sure the test strips were accurate, there has to be chlorine in the school’s tap water, right?

Just need some advice.

You want to test total that will ensure nothing is left. What is the lowest threshold on those strips? Most strips are made for pools or cleaning and dont test low enough for drinking water. Drinking water regulation states that a residual between 0.40 and 4.00 mg/L is within range. A school does not necessarily have to have chlorine in their water, if their an only service connection and serve under 25 people they could not be regulated at all (unlikely but possible). Even if their regulated, if there were no historical bacteria issues they do not have to sanitize the water. If they have a single service connection (their water source only goes into the school) they could also be treating their water via UV instead of chlorine. Btw, I operate water treatment plants for a living

 

[reefiniteasy]

@TJDSEKULA thank you for your knowledge!

Which Hanna chlorine checker should I get?

Total Chlorine Checker
Or
Total Chlorine Checker ULR

 

[DSEKULA]

Np,
the regular one would likely be fine as ppm is a direct translation to mg/L so 0.40ppm=0.40mg/L those are normal drinking water levels. but if you want to test super low as soon as anything comes through the filter the ulr won't hurt. Just realize that to use the ulr on normal tap water you'd likey have to use a dilution 1ml of sample to 9ml of rodi for example and times your reading by 10.

 

[reefiniteasy]

So ideally, use the ULR for testing after the filter and regular checker for the tap?

 

[DSEKULA]

So ideally, use the ULR for testing after the filter and regular checker for the tap?

Yes exactly

 

[reefiniteasy]

So I got my chlorine ULR checker. I tested 17ppb total chlorine. I’m going to change out the carbon block in my RODI unit tomorrow. I’m so glad I got the checker. Who knows how long I would have gone otherwise.

Will I definitely get 0ppb with a new carbon block? Does the carbon remove every bit of the chlorine or will trace amounts always get through?

thank you @TJDSEKULA for all the help.

 

[DSEKULA]

Regrettably no you will not definitely get a 0 with a new carbon block the accuracy of the Hanna meter is .03 so it can be that much off. your 17 is really 16.97-17.03 so you could see as high as a .03 and be truly at 0. You can also read a 0 and really be at .03
The removal of chlorine by carbon is also influenced by pH and temperature along with how pure the water is to begin with. if there are other organics present for example the surface area for oxidizing chlorine will be limited. If the pH or temp changes the reaction may not occur or only remove some of the chlorine. The carbon auctually oxidizes the chlorine it dosent absorb it btw. If your concerned you could always let the water stand for a day with an air stone (oxidizing it out) or add some sodium thiosulfate (dechlorinator).

 

[reefiniteasy]

So, is it safe to say that unless the storage tank sits or dechlorinator is used, there is no way to completely eliminate chlorine?

By the way, my carbon block has been in use since March/April.

If I produced 20 gallons of RODI and an hour later I tested 17ppb, will it test lower tomorrow? Just from sitting over night?

I assume at 17ppb, even though it’s a small amount, it is degrading my RO membrane?

Theoretically if I change to a new block I should be in that 0 to .03 range? Which is completely safe to use? Should I be using dechlorinator on my RODI water anyway? Do people do that?

 

[DSEKULA]

It's possible to completely break down the chlorine with the carbon block and you could definitely test a 0.0
I'd check the accuracy of your meter with water that you know has absolutely no chlorine and see what reading you get (distilled, well water etc) what ever reading you get is comparable to a 0.00 even if the non chlorinated water reads 0.01 then if yours reads a 0.01 I'd consider that a 0.00, I'm also relitvely sure most people don't do that though I do tend to go a bit over board with accuracy due to my career.
You certainly could or should be in the 0.00-0.03 range with a new block I just warn you not to assume you definitely will get a 0 just because there is a new block as there are other factors in play. Yes, if you leave your water sitting the chlorine will naturally oxidize over time, you can dechlorinate rodi water idk if anyone else does but it wouldn't hurt to keep some on hand as an emergency back up. I regularly use chlorine to disinfect qt gear and then dechlorinator to ensure its ready for the next round.

 

[reefiniteasy]

So my next question is, at what point does the chlorine become toxic to the aquarium? Is 17ppb let alone any amount in ppb toxic?
Should I test for chlorine every time I mix up my 5 gallon bucket of saltwater? And use dechlorinator? What do you do?

I think I’m starting to over think this now that I have my Hanna checker.

 

[reefiniteasy]

I tested my RODI storage this morning and it tested 0ppb total chlorine...Awesome! I used 5 gallons of it to mix up a bucket of saltwater for a change. I then turned on the system to refill my storage reservoir and then tested again. I am now getting 2ppb total chlorine, so that is 1.97-2.03, correct? Still not 0 even with a new block... By the time I go to use it, I'm not worried as

Could my old carbon block letting 17ppb through have an effect on the RO membrane? I ask because I usually only get 2-3ppm TDS out of the membrane, and today after I changed the carbon block I was getting 1ppm TDS almost immediately. Is this possible, could 17ppb total chlorine inhibit the function of the RO membrane like that?